During the last year we developed a simple model which quantitatively accounts for the concentration dependence of the thermodynamic and hydrodynamic properties of salt solutions of hemoglobin. The ligand binding equilibria of valence hybrid hemoglobins have been analyzed and shown to be incompatible with a concerted two-state allosteric model. Several new techniques for measuring the oxygen equilibrium of aggregating solutions of sickle hemoglobin have been explored. We have developed a new technique for measuring the equilibrium minimum gelling concentration of sickle hemoglobin solutions. Equilibrium and kinetic data on the binding of insulin to cell surface receptors have been analyzed and reinterpreted. BIBLIOGRAPHIC REFERENCES: Minton, Allen P.: Non-ideality and the thermodynamics of sickle-cell hemoglobin gelation. J. Mol. Biol. 110: 89-103, 1977. Fung, Leslie W.-M., Minton, Allen P., Lindstrom, T. R., Pisciotta, A.V. and Ho, C: Proton nuclear magnetic resonance studies of Hemoglobin M Milwaukee and their implications concerning the mechanism of cooperative oxygenation of hemoglobin. Biochemistry 16: 1452-1462, 1977.